Field of the Invention
The present disclosure relates to liquid crystal display devices, and more particularly, to a 6 bit/8 bit gamma common driving circuit and a method for driving the same, in which a gamma voltage is changed selectively according to a number of received bits by using an R-string for using gamma in common.
Discussion of the Related Art
Recent flat panel displays include liquid crystal display devices, field emission display devices, plasma display panels, and light emitting display devices. Of the flat panel displays, since the liquid crystal display device has excellent resolution, color expression and picture quality, the liquid crystal display device has been applied to note book computers, desk top monitors, and mobile terminals, actively.
The liquid crystal display device includes a liquid crystal panel having a plurality of gate lines and data lines and a matrix of pixels, a gate driver for driving the gate lines at the liquid crystal panel, and a data driver for driving the data lines at the liquid crystal panel.
Each of the pixels in the liquid crystal panel produces a desired color by a combination of red, green, and blue sub-pixels each of which varies an orientation of liquid crystals to control transmissivity of the light in response to a data signal. Each of the sub-pixels has a thin film transistor connected to the gate line and the data line, and a liquid crystal capacitor connected to the thin film transistor. The liquid crystal capacitor has a pixel voltage which is a difference of voltages between the data signal supplied to a pixel electrode and a common voltage supplied to the common electrode charged thereto and drives the liquid crystals according to the pixel voltage charged thus to control the transmissivity of the light.
The data driver converts a digital data signal to an analog data signal, and supplies the analog data signal to the data line at the liquid crystal panel. For this, the data driver has a digital-to-analog converter for converting the digital data signal to the analog data signal. The digital-to-analog converter has an R-string having a plurality of resistors connected in series, and a selection switch circuit for selective forwarding of voltages divided by the R-string according to a digital signal.
However, a related art data driver IC which supplies the data voltages to the data lines uses the R-string different varied with a number of received bits, to sort products thereof in view of the number of the bits receivable thus.
FIG. 1 illustrates a diagram for describing a gamma voltage ratio and an R-string versus received bits at a related art 6 bit data driver IC, and FIG. 2 illustrates a diagram for describing a gamma voltage ratio and an R-string versus received bits at a related art 8 bit data driver IC.
In general, a gradient denotes a quantity of a light a human visual sensation feels divided by grades. According to the Weber's law, the human visual sensation makes non-linear reaction to brightness of the light. Because of this, if the brightness of the light is recorded linearly within a limited information expression quantity, such as k bit/a channel, the brightness of the light recorded thus is felt, not smoothly, but graded, to human eyes. Therefore, in order to show an optimum picture quality within a given information expression quantity, it is required to encode the brightness of the light, non-linearly. For this, an operation is performed for matching a difference between a driving characteristic of the display panel and the human visual sensation characteristic, which is called as gamma correction. In general, in the gamma correction, a plurality of gamma reference voltage values are set, which are fixed according to the display panel characteristic, and the gamma reference voltage values set thus are divided for compensating a gamma value of each of received digital video data.
Referring to FIG. 1, the related art 6 bit data driver IC drives a digital data received in 64 gradients as an analog signal. As shown in FIG. 2, the related art 8 bit data driver IC drives a digital data received in 256 gradients as an analog signal.
That is, the related art data driver IC which supplies a data voltage to each of the data lines uses R-strings varied with the numbers of received bits, to make the products varied with the numbers of received bits.
Consequently, since the number of bits the drive IC can use is fixed, common use of the chip has been impossible due to the variation of the number of bits.